JP2003231914A - Laser hardening method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laser hardening method which can increase the hardening depth without leaving a ferrite structure and can give a good hardened structure without leaving a troostite structure. <P>SOLUTION: In the laser hardening method for hardening the surface of a work by the irradiation with a laser beam, a warmth-keeping heating period A'-C is caused to follow a hardening heating period A-A'. Securing a sufficient heating period necessary for hardening is compatibilized with steep cooling of a work. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser quenching method suitable for, for example, quenching annularly on the outer peripheral surface of a cylindrical member or linearly on the surface of a flat plate-shaped member.

[0002]

2. Description of the Related Art There is a case where it is desired to quench the outer peripheral surface of a cylindrical member such as various rotary shafts in an axial direction at an axially desired position in order to improve fatigue strength and wear resistance. As a quenching method used in such a case, conventionally, there is a method using high frequency induction heating. In this method, it is necessary to place the material to be quenched (workpiece) inside the heating coil, so the heating coil must be replaced or readjusted depending on the size and shape of the workpiece, which is a troublesome point. . Further, it has been extremely difficult to linearly quench the surface of the flat plate member.

Therefore, recently, a quenching method using a laser capable of flexibly adapting to the size and shape of a work has been used (see Japanese Patent Publication No. 63-50404, etc.). FIG. 8 is a schematic explanatory view of a conventional laser hardening method of this type. In this figure, reference numeral 1 denotes a cylindrical work such as a rotating shaft, which is held by a rotatable chuck (not shown) so as to be rotatable around the axis. The laser light 2 is emitted from the side (above in the figure) of the workpiece 1 which is held by the chuck and is in a rotating state. This irradiation is performed while the work 1 is rotating once or a plurality of times as indicated by arrow a.

A curve B in FIG. 9 is a laser light absorptivity curve showing the absorptance of the laser light 2 on the outer peripheral surface ABC of the work 1 irradiated with the laser light 2 in FIG. As can be seen from this curve B, the outer peripheral surface A of the work 1
The absorption rate of the laser beam 2 in -BC is maximum at the irradiation center position of the laser beam 2 (the position just above the work 1 in FIG. 8) B point. The distance decreases from the point B, that is, toward the point A which is the irradiation start position and the point C which is the irradiation end position.

As shown by the curve C in FIG. 10, the absorption rate of the laser beam 2 becomes maximum when the irradiation angle of the laser beam 2 to the outer peripheral surface of the work 1 is 90 °, and becomes smaller as the angle becomes smaller. Because.

Therefore, when the laser beam 2 is irradiated, the temperature at a certain point N on the outer peripheral surface of the work 1 shown in FIG.
It exhibits a change pattern as shown by the curved line in the middle. That is, in FIG. 8, the temperature of the point N rotating and moving in the clockwise direction (arrow A direction) reaches the maximum value after the laser irradiation starts from the point A and reaches the maximum value. When the laser irradiation is finished and the heating is released, The heat at the N point is rapidly cooled by the self-cooling action of being diffused to the surroundings to draw a curve d.

Such a temperature change curve d has a constant temperature necessary for the structural transformation for quenching after its rise.
Here, the period T1 above the A3 transformation point (quenching temperature period) T1
And has a pattern of being rapidly cooled, and as a result, quenching is performed. Such temperature change causes all points (entire circumference) on the outer peripheral surface of the work 1 while the work 1 is rotating.
Then, the outer peripheral surface of the work 1 is subjected to annular quenching.

By the way, the depth of the hardening depth (hardened layer) is related to the length of the hardening temperature period T1 in the temperature change curve of one point N (laser light irradiation portion) on the outer peripheral surface of the work during laser light irradiation. The longer the period T1, the deeper the quenching depth can be. In addition, whether or not a good quenched structure free of a troostite structure and the like remains can be determined by the work 1
Irrespective of whether or not the cooling is rapidly performed, the steeper the falling edge of the temperature change curve, the better the quenched structure can be obtained.

In the conventional laser hardening method, in order to increase the energy absorption rate, as shown in FIG. 8, the laser beam 2 is irradiated onto the work 1 at a vertical angle or at an angle close thereto, and the curve d in FIG. Quenching was performed in the temperature change pattern shown. That is, quenching was achieved in which cooling was performed rapidly after the temperature was raised, and a quenching structure was obtained in which the troostite structure did not remain in the quenched portion of the work 1.

[0010]

However, in the above-described conventional laser hardening method, as can be seen from the curve 2 in FIG. 11, the hardening temperature period T1 is extremely short. Therefore, there is a problem that the inward heating of the work 1 becomes insufficient, the quenching depth becomes shallow, and the diffusion time of carbon in the work 1 is insufficient, so that the ferrite structure remains.

Therefore, in the method shown in FIG. 8, a method of widening the width of the laser beam 2 or slightly lowering the rotation speed of the work 1 has been considered. According to this, the temperature change pattern in the irradiated portion of the laser light 2 of the work 1 is extended as a whole as shown by the curve D'in FIG. 12, and the quenching temperature period T1 is shown in FIG. The curve 2 of Fig. 2 is wider than the period T1. Therefore, the quenching depth is slightly deepened, and the residual ferrite structure is reduced.

On the other hand, on the other hand, the steepness of cooling of the work 1 after the temperature falls below the constant temperature (A3 transformation point) necessary for quenching is lost, that is, the fall of the curve d'is gentle and the work 1 Quenching was incomplete, such as the troostite structure remaining in the quenched portion.

In order to make the fall of the curve d'above sharp, there is a method of increasing the maximum temperature of the laser light irradiation site by increasing the output of the laser light without changing the heating time. According to the above, the surface of the work 1 may be overheated and melted, so that it was not actually adopted.

Therefore, conventionally, the period required for quenching can be sufficiently long and the work 1 can be rapidly cooled, so that the quenching depth can be deepened, and the ferrite structure does not remain, and the troostite structure cannot be obtained. It has been desired to develop a laser hardening method capable of obtaining a good hardened structure with no residue.

The present invention has been made in view of the above demands, and it is possible to secure both a sufficient heating period necessary for quenching and abrupt cooling of a work, which makes it possible to deepen the quenching depth and to obtain a ferrite structure. It is an object of the present invention to provide a laser quenching method in which a good quenching structure can be obtained in which no troostite structure remains and no rusttight structure remains.

[0016]

In order to achieve the above object, the invention according to claim 1 is a laser quenching method of irradiating a work with laser light to quench the surface of the work. It is characterized in that a heat retention and heating period is added following it.

According to a second aspect of the invention, in the invention of the first aspect, when quenching the outer peripheral surface of the work in an annular or arc shape, the work is rotated about the central axis of the outer peripheral surface. While rotating in one direction, a predetermined width within a range from an arbitrary irradiation start position on the circumferential surface to a position advanced in the workpiece rotation direction by a rotation angle of about 90 ° is set as a predetermined width. The outer peripheral surface of the work is irradiated with laser light from a direction parallel to a line connecting the irradiation start position and the center of rotation for quenching.

According to a third aspect of the present invention, in the invention according to the first aspect, when the flat portion of the work is linearly quenched, the flat portion is irradiated with the laser beam irradiated from a substantially vertical direction. It is characterized in that one end of any one of the flat portions is hardened by tilting in a direction of approaching or moving away from the emission source of the laser light with the other end as a fulcrum.

According to a fourth aspect of the present invention, in the first aspect of the present invention, when the flat portion of the work is quenched linearly, the main laser beam is irradiated from a direction substantially perpendicular to the flat portion. Then, the flat portion and / or the both laser lights are linearly moved and quenched so that the sub-laser light is irradiated from the inclined direction to the flat portion.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an explanatory view of an embodiment of a laser hardening method according to the present invention, and FIG. 2 is a view of the work in FIG. 1 viewed from a laser light emitting side (laser focusing lens side). Note that, also in the present embodiment, the case where the outer peripheral surface of the cylindrical work such as the rotating shaft is quenched in an annular shape will be described as an example.

In the figure, reference numeral 1 indicates, for example, a material of S45.
C, a cylindrical work having a diameter of 10 mm, is held by a rotatable chuck (not shown) so as to be rotatable around the axis. The laser light 2 is oscillated by, for example, an LD-pumped YAG laser oscillator 11 having an output of 750 W, and the optical fiber 1
The light is emitted from the condensing lens 13 whose focal length is set to 200 mm through 2 and is continuously irradiated from the side (upper side in FIG. 1) to the workpiece 1 held by the chuck and in the rotating state. .

In this case, the width of the laser beam 2 is about 5 mm, which corresponds to the radius of the work 1, more specifically 5 mm.
It is set to a size slightly smaller than. Further, the laser beam 2 is set so that the center position in the width direction (horizontal direction in FIG. 1) is irradiated to a position deviated from the center position of the work 1 in the rotation direction side.

Here, the laser beam 2 is used by rotating the work 1 in the clockwise direction (direction of arrow A) with the rotation angle of 0 ° right above the work 1 in FIG. 1 (heating start position).
Is a range from the rotation angle of 0 ° to a position of a rotation angle of 90 °, which is advanced by 90 ° in the clockwise direction (the left half side of the work 1 when viewed from the condenser lens 13 side, a range that makes about a quarter round). Has a width W1 as an irradiation region. Further, the laser beam 2 is set so as to be applied to the outer peripheral surface (circumferential surface) of the work 1 from a direction parallel to a line connecting the position of the rotation angle 0 ° and the rotation center O of the work 1. . That is, the irradiation position, the irradiation width, and the irradiation direction of the laser beam 2 with respect to the work 1 are set so that the heat retention heating period, that is, the period for maintaining the temperature at the end of the quenching heating period is added following the quenching heating period. Has been done.

The thickness dimension D1 of the laser beam 2 is the dimension corresponding to the desired quenching width dimension, usually the same dimension as the quenching width dimension, and the axial position of the work 1 irradiated with the laser beam 2 is the quenching dimension. Each is set to the desired position. here,
As shown in FIG. 2, at a substantially central position in the axial direction of the work 1,
The laser light 2 is set to be emitted with a thickness dimension D1 of 3 mm. The laser beam width W1 and the thickness dimension D1 can be changed, for example, by operating the focal length of the condenser lens 13, but the output of the laser beam 2 is constant.

The irradiation of the laser beam 2 is performed while the work 1 is rotated once or a plurality of times. Here, the rotation speed of the work 1 is set to 180 rpm and the irradiation time is set to 3 sec, so that the laser light irradiation is performed 9 times in total.

A curve E in FIG. 3 is a laser light absorptivity curve showing the absorptance of the laser light 2 on the outer peripheral surface AA'-C of the work 1 irradiated with the laser light 2 in FIG. As can be seen from this curve E, the outer peripheral surface A of the work 1
The absorption rate of the laser beam 2 at -A'-C is maximum at the position directly above the work 1 in FIG. 1, that is, at the irradiation start position, point A, and from point A to the irradiation end position, point C. It becomes smaller toward the side. The absorptivity of the laser light 2 is, as shown by the curve C in FIG. 10 above, the irradiation angle of the laser light 2 with respect to the outer peripheral surface of the work 1, that is, the incidence of the laser light 2 with the tangent line at each position on the outer peripheral surface of the work 1. 90 corners
This is because it becomes maximum at 0 ° and becomes smaller (the reflectance of the laser beam 2 becomes larger) as the angle becomes smaller (acute angle).

Therefore, when the laser beam 2 is irradiated, the temperature at a certain point N on the outer peripheral surface of the work 1 shown in FIG. 1 exhibits a change pattern as shown by the curve in FIG. That is, the temperature at point N rotating clockwise in FIG. 1 shows a quenching heating pattern in FIG. 4 in which the laser irradiation starts from point A and rises to reach the maximum value at point A ′ ( The period showing this quenching heating pattern is called the quenching heating period). From point A'to point C that follows this, the irradiation of the laser beam 2 is continued, but the irradiation angle of the laser beam 2 with respect to the outer peripheral surface of the work 1 is gradually reduced, so that overheating of the work 1 is avoided and the temperature drop. Does not occur, that is, a heat retention heating pattern for holding the temperature at the point A ′ is shown (a period showing this heat retention heating pattern is called a heat retention heating period). Then, the irradiation of the laser beam 2 ends at point C,
When the heating is released, the work 1 self-cools to show a steep falling pattern.

Such a temperature change curve has a constant temperature required for structural transformation for quenching after its rise,
Here, the period T1 above the A3 transformation point (quenching temperature period) T1
And has a pattern of being rapidly cooled, and as a result, quenching is performed. Such temperature change causes all points (entire circumference) on the outer peripheral surface of the work 1 while the work 1 is rotating.
Then, the outer peripheral surface of the work 1 is subjected to annular quenching.

As described above, the depth of hardening (hardened layer) is a certain point N on the outer peripheral surface of the work when the laser beam is irradiated.
This is related to the length of the quenching temperature period T1 in the temperature change curve of (laser light irradiation portion), and the longer the period T1, the deeper the quenching depth can be. Further, whether or not a good quenching structure in which a troostite structure or the like does not remain can be obtained depends on whether or not the work 1 is rapidly cooled, the fall of the temperature change curve, specifically, the same as the above temperature. A of change curve
The steeper the falling portion after falling below the 3 transformation point, the better the quenching structure obtained.

In the laser hardening method of the present invention described above,
Since the laser light 2 is applied to the rotation angle region of approximately 90 ° on the rotation direction side in the region of the outer peripheral surface 180 ° of the cylindrical work 1, the laser light absorption rate gradually decreases from the maximum value. Then, the work 1 is heated. Therefore, quenching is performed in a temperature change pattern as shown by the curve in FIG. 4, that is, in a pattern in which the heat retention heating period is added following the quenching heating period.

According to this, the time required for the transformation of the structure for quenching to be higher than a certain temperature can be taken longer, and the quenching depth can be deepened. In addition, since the time of the constant temperature or more is set to be long by maintaining the quenching heating temperature (adding the heat retention heating period), the irradiation position of the laser light 2 is kept at the position shown in FIG. Unlike the method of widening the width or lowering the rotation speed of the work 1, the steepness of cooling is not lost. Therefore, it is possible to prevent the incompletely hardened structure (the troostite structure) from remaining in the hardened portion of the work 1. According to this, the quenching temperature period T1 can be lengthened without overheating and melting the surface of the work 1, the quenching is possible, the ferrite structure does not remain, and the troostite structure does not remain, Good quenching structure can be achieved.

In the above embodiment, the case where the outer peripheral surface of the cylindrical work is quenched in an annular shape, that is, in the range of 360 ° has been described as an example. However, a part or the whole of the work having a circular or arc surface. Alternatively, that is, quenching may be performed within a range of less than 360 ° (arc shape).

Further, the present invention may be used when linearly quenching the flat surface of the work. In FIG. 5, the material is S45.
An example of a case where the flat work 51 of C is quenched linearly in the left-right direction on the upper surface is shown. Here, work 5
Laser light 2 having a predetermined width W2 on the upper surface of
In the state where the upper surface of the workpiece is irradiated from the vertical direction, the workpiece 51 is gradually tilted to a desired angle in the direction of approaching the emission source (not shown) of the laser light 2 with the corner 52 as the fulcrum (see arrow G).
By doing so, quenching is performed. In the method shown in FIG. 5, the workpiece 51 is gradually tilted (see arrow C) in a direction away from an emission source (not shown) of the laser beam 2 with the corner 62 as a fulcrum in the method shown in FIG. , Quenching.

FIG. 7 shows a workpiece 51 using two laser beams, that is, a main laser beam 2a and a sub laser beam 2b.
An example is shown in which quenching is performed in a straight line on the flat portion of. in this case,
The main laser beam 2a is applied to a plane portion (upper surface in the drawing) of the work 51 from a direction substantially vertical, and the sub-laser light 2b is emitted to a plane portion of the same from an inclined direction. Both laser light 2
The irradiation sites of a and 2b are continuous in the hardening direction, and at least one of the laser beams 2a and 2b and the work 51 is linearly moved in the direction in which the sub laser beam 2b is irradiated following the irradiation of the main laser beam 2a. Here, both laser beams 2a,
Quenching is performed by linearly moving 2b in the direction of arrow.

In any of the methods shown in FIGS. 5 to 7, the laser light 2 at the laser light irradiation site on the upper surface of the work 51 is used.
3 has the same absorptivity as that of the curve E in FIG. 3, and the temperature of the laser light irradiation portion has the same change pattern as that of the curve F in FIG. 4, that is, the heat retention heating period is added following the quenching heating period. Quenching is performed according to the pattern. Therefore,
Similar to the method illustrated in FIG. 1, the quenching temperature period T1 can be lengthened without overheating and melting the surface of the work 1, and the quenching is possible and there is no residual ferrite structure. Good structure of hardened structure can be realized without leaving structure. In the example shown in FIG. 7, the degree of heat retention heating depends on the work 51 of the sub-laser light 2b.
Adjustment of the tilt angle with respect to the plane part of the
It can be adjusted by selecting the output of b.

The heat-retaining heating period that follows the quenching heating period by the laser beam is not necessarily limited to the case of using the laser beam, but since quenching heating is performed by the laser beam, it is better to use the laser beam in the same manner. This is advantageous in realizing the present invention. Further, in the above embodiment, a laser oscillator that oscillates continuous light with a constant output is used, but an output variable or pulsed laser light oscillator is used, and the output and pulse period can be appropriately selected according to the work. Good.

[0037]

As described above, according to the invention of claim 1, it is possible to secure a sufficient heating period necessary for quenching and to sharply cool the work, and it is possible to deepen the quenching depth. It is possible to provide a laser hardening method in which a ferrite structure does not remain and a good hardened structure is obtained without leaving a troostite structure. Laser quenching has the advantage that it can be locally and low-quenched, and is therefore particularly effective for quenching small parts, and is also effective for partial quenching of bearings and crankshafts. In such laser quenching, the quenching depth can be increased and a good quenching structure can be obtained.

According to the second aspect of the present invention, in quenching the outer peripheral surface of a work such as a cylindrical body in an annular or arc shape,
The hardening method according to claim 1 can be realized with the positions of the work and the laser light fixed (only by rotating the work) and with the output of the laser light kept constant.

Further, according to the third aspect of the invention, in the case of linear quenching of the flat portion of the work such as a flat plate, the work is simply tilted, and the output of the laser beam is kept constant. Thus, the quenching method of claim 1 can be realized.

Further, according to the invention as set forth in claim 4, for linear quenching to the flat surface portion as well, only the work or the laser beam is linearly moved, and the output of each laser beam is changed. The quenching method according to claim 1 can be realized while keeping it constant.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of an embodiment of a laser hardening method according to the present invention.

FIG. 2 is a view of the work in FIG. 1 viewed from a laser light irradiation side.

FIG. 3 is a graph showing a laser light absorptance on the outer peripheral surface of the work in FIG.

FIG. 4 is a graph showing a temperature change on the outer peripheral surface of the work in FIG.

FIG. 5 is an explanatory diagram of another embodiment (No. 1) of the laser hardening method according to the present invention.

FIG. 6 is an explanatory view of another embodiment (No. 2) of the laser hardening method according to the present invention.

FIG. 7 is an explanatory diagram of another embodiment (No. 3) of the laser hardening method according to the present invention.

FIG. 8 is an explanatory diagram of a conventional method.

9 is a graph showing a laser light absorption rate on the outer peripheral surface of the work in FIG.

FIG. 10 is a graph showing a laser light absorption rate with respect to a laser light irradiation angle.

11 is a graph showing a temperature change on the outer peripheral surface of the work in FIG. 1. FIG.

FIG. 12 is a graph showing a temperature change of a work outer peripheral surface in a conventional method in which a quenching temperature period is extended.

[Explanation of symbols]

1 work 2 laser light A-A 'Quenching heating period A'-C Insulation heating period

Claims (4)

[Claims] 1. A laser quenching method for irradiating a work with laser light to quench the surface of the work, wherein a heat retention heating period is added following the quenching heating period. 2. When the outer peripheral surface of the work is quenched in an annular or arc shape, the work is rotated in one direction with the central axis of the outer peripheral surface as a rotation center, and any irradiation on the peripheral surface is performed. A laser beam having a predetermined width, which is a desired range within the range from the start position to a position advanced by 90 ° in the rotation angle in the rotation direction of the work, is applied to the line connecting the irradiation start position and the rotation center. The laser hardening method according to claim 1, wherein the outer peripheral surface of the work is irradiated with the light from a parallel direction to perform hardening. 3. When linearly quenching a flat surface of a work, one end side of the flat surface is fulcrum and the other end side is a fulcrum with respect to a laser beam irradiated from a direction substantially perpendicular to the flat surface. As a result, quenching is performed by inclining in a direction approaching or moving away from the laser light emission source.
The laser hardening method described in. 4. When quenching a flat surface of a work in a straight line, a sub laser beam is continuously irradiated from a direction inclined to the main laser light which is irradiated from a direction substantially perpendicular to the flat surface. The laser hardening method according to claim 1, wherein the hardening is performed by linearly moving the flat surface portion and / or the both laser lights.